I recently stumbled across this superb little word processor, and I’m just blown away by how good it for being made by one dude for free. It’s like a slimmed down version of Scrivener or Papyrus, with a wonderfully simple and easy to use interface.
It’s open-source, and works on all platforms (Windows, Mac, Linux, including phones and tablets). This lady here does an excellent overview of its features.
If you’re looking for a nice little app for writing, outlining, or planning something, I’d recommend giving it a look.
It works fine in (Android) Firefox, and supports loading from/saving to local files.
I can’t imagine wanting to write a book on my phone though.
Definitely not on a phone, but Android tablets with a keyboard can make decent typing devices.